开玩笑不了解流类型和对象解构？答案

【问题标题】：jest doesn't understand flow types and object destructuring?开玩笑不了解流类型和对象解构？
【发布时间】：2017-05-21 17:51:12
【问题描述】：

我不断收到有关流类型和玩笑的错误：

TypeError: Cannot read property 'returnType' of undefined

  at builder (src/index.js:22:195)
  at Object.<anonymous> (__test__/index.spec.js:6:53)
  at process._tickCallback (internal/process/next_tick.js:103:7)

以下是我的整个设置：

应用代码：

// @flow
type BuilderReturnType = {
    path: string,
    query: string
}

type BuilderOptionsType = {
    returnType?: string
}

export default function builder(path: string, {returnType = 'object'}: BuilderOptionsType): BuilderReturnType {
    const query = {};
    let queryResult = null;
    if (returnType === 'string') {
        queryResult = doSomething(query);
    }
    return {
        path,
        query: queryResult !== null ? queryResult : query
    }
}

.babelrc 配置：

{
    "presets": [
        "es2015", "jest"
    ],
    "plugins": [
        "transform-object-rest-spread",
        "transform-flow-strip-types"
    ],
    "env": {
        "test": {
            "presets": [
                "es2015", "jest"
            ],
            "plugins": [
                "transform-object-rest-spread",
                "transform-flow-strip-types"
            ]
        }
    }
}

jest.json 配置：

{
  "bail": true,
  "verbose": true,
  "collectCoverage": true,
  "coverageDirectory": "./coverage",
  "coverageThreshold": {
    "global": {
      "branches": 100,
      "functions": 100,
      "lines": 100,
      "statements": 100
    }
  },
  "transform": {
    "^.+\\.js$": "<rootDir>/node_modules/babel-jest"
  }
}

似乎同时使用解构和流类型的方法签名存在问题（BuilderOptionsType对象）：

    export default function builder(path: string, {returnType = 'object'}: BuilderOptionsType): BuilderReturnType { ... }

如果我将{returnType = 'object'} 更改为options，然后在方法中进行解构，它似乎完全可以正常工作。考虑到这一点，这是允许同时使用 jest 和 flow 类型的唯一方法吗？我希望能够在签名中解构而不是在方法体中。

【问题讨论】：

标签： javascript babeljs jestjs flowtype

【解决方案1】：

查看您的错误，您可能只是没有将第二个参数传递给函数。如果您调用builder('foo')，您将尝试从undefined 中解构returnType。

要么用第二个参数调用它：builder('foo', {})，要么为参数提供一个默认值：

export default function builder(path: string, {returnType = 'object'}: BuilderOptionsType = {}): BuilderReturnType { ... }

【讨论】：

啊，我觉得{returnType = 'object'}: BuilderOptionsType够了